Separation problems, such as the separation of a dispersed phase from a continuous phase, often occur in industry. Such separation may be part of manufacturing process, may be the isolation step of a starting material or end-product, or may be a step of a cleaning process.
Magnetic separation techniques in various forms are known in which contaminating oil is removed from water (e.g. after oil spills) circumventing the problems of water/oil separation using gravitational forces only. This is done by using magnetic particulates which have surfactants, polymers, dispersing agents or other oeleophilic chemicals attached or adsorbed to the particle surfaces.
GB1439031 proposes the use of magnetic fluids for cleaning up oil spills and describes the use of magnetic iron oxide particles produced by the precipitation of iron chlorides by the use of ammonium hydroxide with an oil soluble dispersing agent adsorbed to the surface of the particles.
GB2319023 describes the use of magnetite (Fe3O4) particulates which have a surfactant such as polyoxyethylene nonylphenylether adsorbed to the particle surface allowing a dispersion in organic solutions.
JP63042751 describes the use of a magnetic polymer affiliated with oil and trapping the oil to the polymer and attracting it with a magnet. The described magnetic polymers consist of a magnetite or cobalt ferrite (CoFe2O4) core with diameters below 200 nanometers deposited onto a polymer having a high affinity with oil.
US20050139550 describes the use of iron particles with a size between 1 and 100 micrometers (equivalent to a specific surface area between 0.6 m2/g and 0.006 m2/g) which have been made hydrophobic by reacting the iron particles with organic compounds having oleophilic chain ends such as saturated fatty acids.
It is believed that, an ideal magnetic separation process is characterized by the utilization of magnetic particles of low cost, high selectivity to one phase, low particle size and excellent magnetic properties. Theses properties should result in a maximum active surface area available for the attraction of the dispersed phase per magnetic unit. Prior art, as disclosed above, suffers from one or more disadvantages. Thus, the known techniques utilize either large particulates or materials of poor magnetic properties (e.g. saturation magnetization<100 A m2/kg) and surface modifications of large (>C6) oleophilic adsorbants coating the particles further diminishing the overall particle magnetization and increasing the overall particle diameter. Large particles are not desired as they also slow down the movement of the particles in the liquid.